Polysilane composition for forming a coating suitable for bearing a metal pattern, metal pattern forming method, wiring board preparing method

ABSTRACT

A metal pattern is prepared by applying a polysilane composition comprising a polysilane, a carbon functional silane, and a solvent onto a substrate to form a patterned coating of the polysilane composition, attaching catalytic metal nuclei to the patterned coating, and immersing the substrate in an electroless plating bath for thereby chemically depositing a metal film on the patterned coating.

This invention relates to a polysilane composition for forming a coatingsuitable for bearing a metal pattern, and a metal pattern forming methodusing the same. It also relates to a method for preparing a wiringboard.

BACKGROUND OF THE INVENTION

Substrates having metal patterns formed thereon are used in a variety ofapplications, for example, as printed circuit boards and comb-shapedelectrode substrates for sensors. Metallization on such substrates isgenerally carried out by vapor phase methods such as CVD and wet methodsas typified by plating methods. The metal is then patterned by a complexmethod which generally uses a resist material and involves exposure anddevelopment steps.

To eliminate such complication, Whiteside et al. proposed a novel metalpatterning procedure. This procedure is to form a metal pattern byimmersing a rubber material having an irregular surface in a dispersionof palladium colloid. The rubber material is then pressed against asubstrate whereby the palladium colloid on raised portions istransferred to the substrate. The substrate is then immersed in anelectroless or chemical plating bath whereby a metal deposits only onthe palladium colloid- bearing areas. (See Langmuir 1996, 12,1375-1380.)

Unfortunately, this procedure has the drawback that the palladiumcolloid is very unstable. Typically, a surfactant such as tetraammoniumhalide is added to the palladium colloid for stabilizing the colloid. Anattempt to apply the palladium colloid by an imprinting, ink jetprinting or lithographic process fails because of coagulation andprecipitation of the palladium colloid. No uniform metal pattern isformed and the adhesion between the substrate and the metal isinsufficient.

Printed circuit boards now encounter a strong need for higher densitybecause of the widespread use of ultra-thin equipment. In prior artprinted circuit boards, after a copper foil is bonded to a resinsubstrate with an adhesive, patterning is carried out using a resist(subtractive process). However, a proper adhesive must be used dependingon a particular resin selected from among phenolic resins, polyesterresins, epoxy resins, polyimide resins, and bismaleimide triazineresins. A complex bonding process is necessary. The bond strength is notfully high.

In recent years, a need to form a finer metal pattern promotes researchefforts on the additive process of metallizing a resin substrate, ratherthan the subtractive process suffering from the thinning of a metal filmby over-etching, so that the additive process may be employed on acommercially acceptable level. For the additive process, however, animprovement in the adhesion between the resin substrate and themetallization is of significance.

For logic devices and system LSI's, there is a strong need to increasethe degree of integration and operational speed of circuits in order torealize high-speed electronic equipment. In this regard, an attention ispaid to copper as a low resistance wiring material. In the prior artsemiconductor device manufacture, aluminum is used as the material forforming fine metal circuits on semiconductor and a CVD process is usedfor its application. Copper is more difficult to work than aluminum.Then there is an urgent desire to establish a micro-wiring technique forcopper. One solution to the above-described problem is electrolyticplating. It has been studied to apply electrolytic plating to the copperwiring process on a commercially acceptable level (see monthlySemiconductor World, February 1998, pp. 82-85).

However, the electrolytic plating has the drawback that the thickness ofmetal coating locally varies and is not reproducible, which becomes aneck to mass manufacture. When the electrolytic plating is combined witha resist material and resist process necessary to form a fine metalpattern in a mass scale, optimum conditions of the electrolytic platinghave not been fully established.

Polysilane is an interesting polymer because of its UV absorptionproperties due to the metallic property and unique electrondelocalization of silicon as compared with carbon, as well as its highheat resistance, flexibility, and good thin film forming properties.Active research efforts have been made on polysilane for the purpose ofdeveloping a photoresist capable of forming a micropattern at a highprecision (see, for example, JP-A 6-291273 and 7-114188).

Finding that a palladium colloid forms when a polysilane is contactedwith a solution of a palladium salt, and that UV irradiation causes theconversion of polysilane into polysiloxane, the inventors proposed apattern forming method. The inventors also found that a metal patterncan be formed by combining such characteristics of a polysilane thinfilm with electroless plating catalyzed by palladium colloid (JP-A10-325957). However, this method still requires the steps of lightirradiation and exposure.

JP-A 5-72694 discloses the use of a polysilane in a method for preparinga semiconductor integrated circuit. This method is characterized in thata film of polysilane optionally doped with iodine is used as aconductive layer and a siloxane layer converted from polysilane by lightirradiation is used as an insulating layer. It has thus beencontemplated to apply the polysilane or polymer having a Si-to-Si bondas conductive material.

However, the semiconductor integrated circuit obtained by the abovemethod has the problems that the conductive areas consisting solely ofpolysilane are not fully conductive and the use of potentially corrosiveiodine becomes a serious obstacle to the application of polysilane toelectronic material. Additionally, since the polysilane which is likelyto convert into siloxane upon exposure to moisture, oxygen or light inthe ambient atmosphere is used as conductive material, its applicationto electronic material requiring reliability encounters greatdifficulty.

JP-A 57-11339 discloses a method for forming a metal image by exposing acompound having a Si-to-Si bond to light and contacting it with a metalsalt solution. When the compound having a Si-to-Si bond is contactedwith the metal salt solution, the metal salt is reduced to the metal.Utilizing this phenomenon, a metal layer is formed in the unexposedarea. To define a definite image by this method, the exposed area mustbe completely deprived of reducing property, which requires to irradiatea large quantity of light. Upon light exposure, the polysilane isconverted into siloxane. Once a finely defined circuit is formed by UVirradiation, it becomes very difficult to further convert the siloxaneinto a polycarbosilane or polysilazane which is an insulating ceramicprecursor having heat resistance and toughness.

There is a desire to have a technique of manufacturing a wiring board ofhigh quality in an industrially advantageous manner.

SUMMARY OF THE INVENTION

One object of the invention is to provide a method of forming a metalpattern on a substrate by a simple step such as a conventionallyemployed imprinting, ink jet printing or lithographic process without aneed for light irradiation and exposure. Another object is to provide apolysilane composition used in the method for forming a coating suitablefor bearing a metal pattern.

A further object is to provide a method for preparing a wiring boardhaving a pattern of highly conductive areas and insulating areas throughsimple and inexpensive steps so that the wiring board may have high heatresistance and pattern definition and be used in a variety ofapplications in the electric, electronic and communication fields.

In a first embodiment of the invention, there is provided a polysilanecomposition for forming a coating suitable for bearing a metal patternthereon, comprising a polysilane, a carbon functional silane, and asolvent.

In a second embodiment of the invention, there is provided a metalpattern forming method comprising the steps of:

applying the above-defined polysilane composition onto a substrate by animprinting, ink jet printing or lithographic process, to form apatterned coating of the polysilane composition,

attaching catalytic metal nuclei for electroless plating to thepatterned coating, and

immersing the substrate in an electroless plating bath and depositing anelectroless plating film on the patterned coating.

The inventors have found that a composition comprising a polysilane anda carbon functional silane (sometimes abbreviated as CF silane) forms acoating which readily captures a palladium salt and thus ensures that anelectroless plating film forms thereon with a firm bond. The coatingitself has a high strength. Using the polysilane composition, apatterned film of polysilane can be easily formed on a substrate by animprinting, ink jet printing or lithographic process. After catalyticmetal nuclei such as palladium nuclei are distributed on the patternedcoating, the substrate is immersed in an electroless plating bath. Inthis way, a metal pattern can be formed by a simple inexpensive processwithout a need for exposure and development steps.

In a third embodiment of the invention, there is provided a method forpreparing a wiring board comprising the steps of:

(1) forming a carbon functional silane-containing polysilane thin filmon a substrate and contacting a palladium salt with a surface of thepolysilane thin film to form a palladium colloid layer thereon,

(2) forming a photosensitive resin layer on the polysilane thin filmhaving the palladium colloid layer, selectively irradiating light to thelayer, and developing the layer, to thereby form a predetermined patternof channels in the photosensitive resin layer so that the polysilanethin film having the palladium colloid layer is exposed within thechannels, and

(3) contacting an electroless plating solution with the polysilane thinfilm having the palladium colloid layer exposed within the channels, forthereby forming a conductive metal layer within the channels.

In a fourth embodiment of the invention, there is provided a method forpreparing a wiring board comprising the steps of:

(I) forming a SiH group-containing polysilane thin film on a substrateand irradiating light to the thin film for crosslinking the polysilanefor thereby insolubilizing the polysilane,

(II) forming a photosensitive resin layer on the crosslinked polysilanethin film, selectively irradiating light to the layer, and developingthe layer, to thereby form a predetermined pattern of channels in thephotosensitive resin layer so that the crosslinked polysilane thin filmis exposed within the channels, and

(III) contacting a palladium salt with the crosslinked polysilane thinfilm exposed within the channels to form a palladium colloid layer andcontacting an electroless plating solution for thereby forming aconductive metal layer within the channels.

The inventors found that when a polysilane is previously irradiated withUV radiation, the polysilane is converted into a polysiloxane so thatthe surface is changed to be polar. When this polysiloxane is contactedwith a palladium salt solution, a palladium colloid can be formed, whichenables pattern formation. As long as the palladium colloid is attachedto the surface of a resin coating, the electroless plating methodpermits a metal film of uniform thickness to form on a variety ofresins. A metal pattern of copper can be formed by combining theabove-described characteristics of a polysilane thin film withelectroless plating catalyzed by palladium colloid. A circuit boardhaving improved heat resistance and pattern definition can bemanufactured by a simple inexpensive process. This process is proposedin Japanese Patent Application No. 10-94111.

Continuing the research, the inventors found that in a method forpreparing a circuit board utilizing a metal pattern, the metal patternsometimes has an unsatisfactory adhesion to the substrate. When themetal pattern is formed utilizing the optically defined resist pattern,the metal area partially spreads with the progress of metal deposition.Then, the pattern resulting from the resist becomes far fromsatisfactory.

Then the inventors made further research to produce a wiring board whichhas improved adhesion between a metal pattern and a substrate and animproved pattern profile. In the wiring board preparing method accordingto the third embodiment of the invention, a composition comprising apolysilane and a CF silane as main components is applied onto asubstrate to form a CF-silane containing polysilane thin film having animproved film strength. When the polysilane thin film is contacted witha palladium salt, the palladium salt is readily captured by thepolysilane thin film to form a palladium colloid layer thereon. Then aphotosensitive resin layer is formed on the palladium colloid layer forforming a pattern of channels. The CF-silane containing polysilane thinfilm is exposed within the channels. Then electroless plating is carriedout. The adhesion between the conductive metal layer of copper or thelike formed by the electroless plating and the substrate is strong.Since the conductive metal layer is formed within the channels, there isno risk that the conductive metal area spreads out.

In the wiring board preparing method according to the fourth embodimentof the invention, a polysilane undergoes crosslinking reaction underirradiation of light such as ultraviolet radiation and becomes insolublein solvents. Even after being crosslinked by light irradiation, thispolymer is effective for readily reducing a palladium salt in contacttherewith, to form a palladium colloid. A photosensitive resin layer isthen formed on the crosslinked polysilane thin film to define apredetermined pattern of channels so that the crosslinked polysilanethin film is exposed within the channels. After a palladium colloidlayer is formed thereat, electroless plating is carried out to form aconductive metal layer as in the third embodiment. In this way, therecan be formed a metal pattern which has improved adhesion to thesubstrate, and is stable and free of the risk that the conductive metalarea spreads out. A conductive wiring pattern having satisfactorydefinition can be manufactured by a simple inexpensive process.

The wiring board preparing method of the invention can fabricate,through simple and inexpensive steps, a wiring board which has high heatresistance and a high degree of pattern definition and can be used in avariety of applications in the electric, electronic and communicationfields.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a wiring board preparing methodaccording to the third embodiment of the invention.

FIG. 2 schematically illustrates a wiring board preparing methodaccording to the fourth embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The polysilane composition according to the invention is defined ascomprising a polysilane, a carbon functional silane (CF silane), and asolvent in which these components are dissolved. The composition iseffective for forming a coating suitable for bearing a metal patternthereon.

The polysilane used herein may be of any type as long as it can form acoating. Preferably, the polysilane is of the following formula (1):

(R¹ _(m)R² _(n)X_(p)Si)_(q)  (1)

wherein R¹ and R² each are hydrogen or a substituted or unsubstitutedmonovalent hydrocarbon group, X is hydrogen or a substituted orunsubstituted monovalent hydrocarbon group, alkoxy group or halogenatom, m is a number of 0.1 to 2, n is a number of 0 to 1, p is a numberof 0 to 0.5, the sum of m+n+p is from 1 to 2.5, and q is an integer of 4to 100,000.

The monovalent hydrocarbon groups represented by R¹ and R² includesubstituted or unsubstituted aliphatic, alicyclic and aromatichydrocarbon groups. Preferred aliphatic and alicyclic hydrocarbon groupsare those of 1 to 12 carbon atoms, especially 1 to 8 carbon atoms, forexample, but not limited to, alkyl and cycloalkyl groups such as methyl,ethyl, propyl, butyl, pentyl, hexyl, cyclopentyl and cyclohexyl.Preferred aromatic hydrocarbon groups are those of 6 to 14 carbon atoms,especially 6 to 10 carbon atoms, for example, but not limited to, arylgroups such as phenyl, tolyl, xylyl and naphthyl and aralkyl groups suchas phenylethyl. The substituted hydrocarbon groups are theabove-described unsubstituted aliphatic, alicyclic and aromatichydrocarbon groups in which some or all of the hydrogen atoms arereplaced by halogen atoms, alkoxy groups, amino groups, aminoalkylgroups and other substituents, for example, but not limited to,monofluoromethyl, trifluoromethyl, p-dimethylaminophenyl, andm-dimethylaminophenyl.

X represents groups as defined for R¹ or alkoxy groups or halogen atoms.Exemplary alkoxy groups are those of 1 to 4 carbon atoms, such asmethoxy and ethoxy. Preferred halogen atoms are fluorine, chlorine andbromine. Of these, chlorine atoms, methoxy and ethoxy groups arepreferable. It is noted that the group represented by X is effective forpreventing the polysilane coating from separating from the substrate andthus improving the adhesion of the coating to the substrate.

The letters m, n and p are numbers satisfying 0.1≦m≦2, preferably0.5≦m≦2, 0≦n≦1, preferably 0.5≦n≦1, 0≦p≦0.5, preferably 0≦p≦0.2, and1≦m+n+p≦2.5, preferably 1.5≦m+n+p≦2.5. The letter q is an integer of4≦q≦100,000, preferably 10≦q≦10,000.

The polysilane of formula (1) can be readily synthesized, for example,by adding an alkali metal catalyst (e.g., metallic sodium) to an organicsolvent (e.g., toluene) in a nitrogen stream, and agitating the mixtureat a high speed while heating, thereby effecting dispersion. To thedispersion, a silicon compound (e.g., dichloroorganosilane) is slowlyadded dropwise in an amount of about 1 mol of the silicon compoundrelative to 2 or 3 mol of metallic sodium. The reaction solution isagitated for 1 to 8 hours until the silicon compound disappears. Afterthe completion of reaction, the reaction solution is allowed to cooldown, filtered to remove the salt, and concentrated.

The CF silane is preferably of the following general formula (3):

Y—(CH₂)_(b)—SiR_(a)(OR)_(3−a)  (3)

wherein Y is a functional group such as a vinyl, epoxy, amino, mercapto,methacryloxy or acryloxy functional group, R is a substituted orunsubstituted monovalent hydrocarbon group, b is an integer of 0 to 3,and a is equal to 0 or 1.

R represents monovalent hydrocarbon group as defined above for R¹ andR², preferably alkyl groups of 1 to 5 carbon atoms. An exemplary vinylfunctional group is CH₂═CH—, exemplary epoxy functional groups areγ-glycidoxy and 3,4-epoxycyclohexyl, exemplary amino functional groupsare NH₂— and NH₂CH₂CH₂NH—, an exemplary mercapto functional group ismercapto, exemplary methacryloxy and acryloxy functional groups aremethacryloxy and acryloxy.

Illustrative examples of the CF silane of formula (3) includevinyltrimethoxysilane (KBM-1003), vinyltriethoxy-silane (KBE-1003),β-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane (KBM-303),γ-glycidoxypropyl-trimethoxysilane (KBM-403),N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane (KBM-602),N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane (KBM-603),γ-aminopropyltrimethoxysilane (KBM-903), andγ-aminopropyltriethoxysilane (KBE-903), all commercially available underthe indicated trade name from Shin-Etsu Chemical Co., Ltd. Of these,amino group-containing CF silanes: KBM-602, KBM-603, KBM-902, KBM-903,KBE-602, KBE-603, KBE-902 and KBE-903 are preferable.

An appropriate amount of the CF silane added is 0.01 to 200 parts,especially 0.1 to 10 parts by weight per 100 parts by weight of thepolysilane. Outside the range, a less amount of the CF silane would failto achieve sufficient adhesion whereas an excessive amount of the CFsilane would sometimes adversely affect film formation and rather lowerthe adhesion.

The addition of the CF silane improves the strength of a polysilanecoating and permits the polysilane coating to readily capture apalladium salt when the palladium salt is brought into contacttherewith, which in turn, enables that a metal film (e.g., of copper)having improved adhesion to the substrate is formed by electrolessplating.

The polysilane and the CF silane are dissolved in a suitable organicsolvent. Examples of the solvent used herein include aromatichydrocarbon solvents such as benzene, toluene and xylene, ether solventssuch as tetrahydrofuran and dibutyl ether, alcohol solvents such asmethanol and ethanol, alkoxyethanol solvents such as ethyl cellosolveand methyl cellosolve, ketone solvents such as acetone and methyl ethylketone, ester solvents such as ethyl acetate, butyl acetate, methyllactate, and ethyl lactate, and ether ester solvents such as PGMEA. Anappropriate amount of the solvent used is about 10 to about 10,000 partsby weight per 100 parts by weight of the silicon components (polysilaneand CF silane) combined.

To the composition, inorganic powders such as fumed silica andalkoxysilanes such as tetraethoxysilane may be added if necessary.

The metal pattern forming method according to the second embodiment ofthe invention uses the above-defined polysilane composition and involvesthe steps of:

(1) forming a polysilane pattern on a substrate by an imprinting, inkjet printing or lithographic process, and

(2) immersing the substrate in a solution of a catalytic metal salt suchas a palladium salt and then in an electroless plating bath fordepositing a metal on the pattern.

If desired, the substrate resulting from step (1) and/or (2) issubjected to UV irradiation or heating for improving the adhesionbetween the metal and the substrate. There is obtained a substratehaving a metal pattern formed thereon and firmly adhered thereto.

The substrate used herein may be made of insulating materials such asglass, ceramics and plastics, semiconductors such as silicon, andconductors such as copper. Among these, resins or plastics such asphenolic resins, polyester resins, epoxy resins, polyimide resins, andbismaleimide triazine resins are preferable.

The imprinting, ink jet printing and lithographic processes are includedin conventional printing processes. They have the following featureswhen used in forming a patterned coating of polysilane on a substratesurface.

The imprinting process involves immersing a rubber plate having apattern of raised portions in a polysilane composition, and pressing therubber plate against a substrate for thereby transferring the siliconcomponents (polysilane and CF silane) on the raised portions to thesubstrate. Although the number of printable members is small, theimprinting process is advantageous in that a metal pattern can be formedeven on a curved surface.

The ink jet printing process is by ejecting toward a substrate dropletsof the polysilane composition having a size of a picoliter order throughnozzle orifices in accordance with record signals to form a pattern.This process is advantageous in forming a micropattern.

The lithographic process uses a lithographic plate having image areasand non-image areas arranged on a support in a planar fashion. When thepolysilane composition is supplied to the surface of the plate, thesilicon components (polysilane and CF silane) adhere to only thelipophilic image areas. This process is advantageous in operation,economy and the number of printable members.

After a pattern of silicon components (polysilane and CF silane) isformed on a substrate by any of the above- described processes, thepattern is preferably dried by allowing the substrate to stand for sometime in a dry atmosphere or keeping the substrate in vacuum at atemperature of about 40 to 150° C. The polysilane composition usedpreferably has a concentration of 0.1 to 50% by weight whereby a patternof silicon components (polysilane and CF silane) is formed to athickness of 0.01 to 100 μm.

Next, the substrate having a pattern of silicon components formedthereon is immersed in a solution of a catalytic metal salt such as apalladium or silver salt and then in an electroless plating solution.

The palladium salt used herein contains Pd²⁺ and is generallyrepresented by Pd—Z₂ wherein Z is a halogen such as Cl, Br or I,acetate, trifluoroacetate, acetylacetonate, carbonate, perchlorate,nitrate, sulfate or oxide. Preferred exemplary palladium salts arePdCl₂, PdBr₂, PdI₂, Pd(OCOCH₃)₂, Pd(OCOCF₃)₂, PdSO₄, Pd(NO₃)₂, and PdO.A halide such as hydrochloric acid or sodium chloride may be added tothe palladium salt solution in order to enhance the stability thereof.

For the solution, there is used a solvent in which the palladium salt ishighly soluble and which does not dissolve or attack the pattern ofsilicon components. Exemplary solvents include water, ketones such asacetone and methyl ethyl ketone, esters such as ethyl acetate, alcoholssuch as methanol and ethanol, and aprotic polar solvents such asdimethylformamide, dimethyl sulfoxide and hexamethylphosphoric triamide,as well as nitromethane and acetonitrile. Among others, water is mostpreferable.

The substrate is immersed in the palladium salt solution for about 1second to about 10 minutes, washed with water and dried. There isobtained the substrate on which the palladium salt has been reduced intopalladium particles on the polysilane pattern surface. If desired, thesubstrate is heat treated at 40 to 200° C. for promoting the reductioninto palladium on the polysilane surface. Drying is generally effectedat 10 to 200° C. under atmospheric pressure or vacuum.

Next, the structure is immersed in an electroless plating solution, fromwhich a metal film deposits while palladium serves as the catalyst.

The electroless or chemical plating solution used herein is preferably asolution containing a metal ion such as copper, nickel, palladium, gold,platinum or rhodium. The electroless plating solution is generallyprepared by formulating in water a water-soluble metal salt, a reducingagent (e.g., sodium hypophosphite, hydrazine, sodium boron hydride ordimethylaminoboran), and a complexing agent (e.g., sodium acetate,phenylenediamine or sodium potassium tartrate). Suitable electrolessplating solutions are commercially available at reasonable costs.

Appropriate contact conditions with the electroless plating solutioninclude a temperature of 15 to 120° C., especially 25 to 85° C. and atime of 1 minute to 16 hours, especially 10 to 60 minutes. It ispractical to deposit a metal film to a thickness of 0.01 to 100 μm,especially 0.1 to 20 μm although the thickness varies with a particularpurpose.

After the electroless plating, the structure is heated for improving theadhesion between the metal and the substrate, if desired. For example,the substrate is heated in an inert atmosphere such as argon or invacuum, at a temperature of 60 to 300° C. for about 1 minutes to about24 hours. Then the metal film resulting from electroless plating has ahigher conductivity and hardness and better adhesion to the substrate.

Accordingly, the invention is successful in forming an adherent metalpattern by way of an imprinting, ink jet printing or lithographicprocess which is a simple inexpensive process eliminating a need forexposure and development steps. The metal pattern forming method of theinvention can form on any type of substrate a metal pattern havingimproved adhesion between the metal and the substrate by a simpleinexpensive process. Since the metal patterns can find use as printedcircuit boards, flexible switches, battery electrodes, solar batteries,sensors, antistatic protective films, electromagnetic shield casings,integrated circuits, motor casings, and flat display panels, theinventive method is useful in the electric, electronic and communicationfields.

Next, the method for preparing a wiring board according to the third andfourth embodiments of the invention is described.

The method according to the third embodiment is to prepare a wiringboard through the following successive steps (1) to (3). There isobtained a printed wiring board having a fine metal pattern featuringimproved adhesion between the substrate resin and the metal.

The method according to the third embodiment includes the steps of:

(1) forming a CF-silane containing polysilane thin film on a substrateand contacting a palladium salt with a surface of the polysilane thinfilm to form a palladium colloid layer thereon,

(2) forming a photosensitive resin layer on the polysilane thin filmhaving the palladium colloid layer, selectively irradiating light to thelayer, and developing the layer, to thereby form a predetermined patternof channels in the photosensitive resin layer so that the polysilanethin film having the palladium colloid layer is exposed within thechannels, and

(3) contacting an electroless plating solution with the polysilane thinfilm having the palladium colloid layer exposed within the channels, forthereby forming a conductive metal layer within the channels.

Referring to FIG. 1, step (1) includes forming a CF-silane containingpolysilane thin film 2 on a substrate 1 and contacting a palladium saltwith a surface of the polysilane thin film 2 to form a palladium colloidlayer 3 thereon.

The polysilane and CF silane used in forming the CF-silane containingpolysilane thin film on the substrate are preferably those of formulae(1) and (3) defined above, respectively.

The substrate on which the CF-silane containing polysilane thin film isto be formed may be made of insulating materials such as quartz glass,ceramics, plastics, and resins, semiconductors such as silicon, andconductors such as copper. Among these, resins or plastics such asphenolic resins, polyester resins, epoxy resins, polyimide resins, andbismaleimide triazine resins are preferable.

In forming the CF-silane containing polysilane thin film, any desiredtechnique may be used, for example, conventional polysilane thin filmforming techniques such as spin coating, dipping, casting, vacuumevaporation and Langmuir-Blodgett (LB) techniques. Preferred is the spincoating technique including mixing a polysilane with a CF silane,dissolving them in a suitable solvent, and applying the solution to thesubstrate while rotating the substrate at a high speed.

In connection with the spin coating technique used in forming theCF-silane containing polysilane thin film, the solvent in which thepolysilane and CF silane are dissolved may be selected from aromatichydrocarbon solvents such as benzene, toluene and xylene, and ethersolvents such as tetrahydrofuran and dibutyl ether. The solvent ispreferably used in such amounts that the solution may have a polysilaneplus CF silane concentration of 1 to 20% by weight. After the CF-silanecontaining polysilane thin film is formed, it is preferably dried byallowing it to stand for some time in a dry atmosphere or keeping it atabout 40 to 60° C. in vacuum. In step (1), the CF-silane containingpolysilane thin film formed on the substrate preferably has a thicknessof 0.01 to 100 μm, especially 0.1 to 10 μm.

Since the thin film formed on the substrate contains the polysilane andCF silane as main components, the film not only has a high strength, butalso readily captures a palladium salt when the palladium salt isbrought into contact therewith. Thus a palladium colloid layer isreadily formed on the polysilane thin film. This, in turn, enables thata conductive metal layer (e.g., of copper) having improved adhesion tothe substrate is formed by electroless plating.

Next, the CF-silane containing polysilane thin film formed on thesubstrate is contacted with a palladium salt. Contact is preferablyeffected by treating the substrate with a solution containing apalladium salt. The palladium salt used herein contains Pd²⁺ and isgenerally represented by Pd—Z₂ wherein Z is a halogen such as Cl, Br orI, acetate, trifluoroacetate, acetylacetonate, carbonate, perchlorate,nitrate, sulfate or oxide. Preferred exemplary palladium salts arePdCl₂, PdBr₂, PdI₂, Pd(OCOCH₃)₂, Pd(OCOCF₃)₂, PdSO₄, Pd(NO₃)₂, and PdO.

For contacting the thin film with the palladium salt, a solutiontechnique is preferably employed. The solution technique includesdissolving or dispersing the palladium salt in a suitable solvent andimmersing in the solution or dispersion the substrate having theCF-silane containing polysilane thin film formed thereon.

In the solution technique, there is used a solvent in which thepalladium salt is highly soluble and which does not dissolve theCF-silane containing polysilane thin film. Exemplary solvents includewater, ketones such as acetone and methyl ethyl ketone, esters such asethyl acetate, alcohols such as methanol and ethanol, and aprotic polarsolvents such as dimethylformamide, dimethyl sulfoxide andhexamethylphosphoric triamide, as well as nitromethane and acetonitrile.Among others, water and alcohols such as ethanol are most preferable. Ahalide such as hydrochloric acid or sodium chloride may be added to thepalladium salt solution in order to enhance the stability thereof.

The CF-silane containing polysilane thin film is preferably immersed inthe palladium salt solution or dispersion for about 1 second to about 10minutes. The immersion is preferably followed by drying. Then, thepalladium salt is reduced into palladium particles on the surface of theCF-silane containing polysilane thin film. There is obtained thesubstrate having a palladium colloid layer formed thereon. After thecontact with the palladium salt, if desired, the substrate Is heattreated at 40 to 200° C. for promoting the reduction of the palladiumsalt into palladium on the CF-silane containing polysilane thin filmsurface. Drying is generally effected at 10 to 200° C. under atmosphericpressure or vacuum.

In the subsequent step (2), a photosensitive resin layer 4 is formed onthe palladium colloid layer 3. The photosensitive resin layer 4 isselectively irradiated with light and developed to form a predeterminedpattern of channels 5 (only one channel is shown) in the photosensitiveresin layer 4. The polysilane thin film 2 having the palladium colloidlayer 3 is exposed within the channel 5, forming a pattern latent image.

For the photosensitive resin layer, either a positive resist or anegative resist may be used. In general, using a variety of existingphotosensitive resins such as novolac-photoacid generator systems,chemically amplified silicon polymer systems, and polysilane systemswhich are known as positive working resist material, a layer may beformed in a conventional manner. The invention favors the use ofpolysilane resist materials, but not limited thereto.

In step (2), a photomask 6 of a predetermined pattern is positioned overthe photosensitive resin layer 4 on the substrate 1. UV or visible lightis irradiated from a suitable light source to the photosensitive resinlayer 4 through the mask 6. Then, in the case of positive resist, onlythe exposed area of the photosensitive resin layer is converted to besoluble in a suitable solvent whereupon development is effected with thesolvent to form the predetermined pattern of channels 5. The CF-silanecontaining polysilane thin film 2, specifically the palladium colloidlayer 3, becomes exposed in the channels 5. The thickness of thephotosensitive resin layer is desirably approximate to that of a metalthin film to be formed, typically 0.1 to 10 μm. Since the CF-silanecontaining polysilane film absorbs light or UV radiation and providesanti-reflection effect in the exposure step, the pattern shape is wellretained.

The light source used herein may be a UV light source or visible lightsource. Illustrative examples are continuous spectrum light sources suchas hydrogen discharge lamps, rare gas discharge lamps, tungsten lamps,and halogen lamps, lasers such as KrF and ArF lasers, and discontinuousspectrum light sources such as mercury lamps. A choice of the lightsource depends on the type of photosensitive resin. Mercury lamps havinga radiation source of 248 to 254 nm in wavelength are preferable becauseof low costs and ease of handling. The light source preferably has alight quantity of 0.01 to 10 mJ/cm², especially 0.1 to 1 mJ/cm², perphotosensitive resin layer thickness of 0.1 μm. If the light quantity isbelow the range, the underlying CF-silane containing polysilane thinfilm would be insufficiently exposed. A light quantity above the rangewould cause the CF-silane containing polysilane to be converted into asiloxane having no palladium reducing capability. These situations aredetrimental to the subsequent formation of a satisfactory metal pattern.

After the light exposure, development is carried out. That is, theexposed area (in the case of positive resist) or unexposed area (in thecase of negative resist) is removed using a developer. The developerused herein is a solution which can dissolve away only the exposed area(in the case of positive resist) or unexposed area (in the case ofnegative resist). It may be either an organic solvent or an aqueous basesolution. By this development, the predetermined pattern of channels 5is formed in the photosensitive resin layer 4. The CF-silane containingpolysilane thin film 2 having the palladium colloid layer 3 is exposedwithin the channel 5.

In step (3), an electroless plating solution is contacted with theCF-silane containing polysilane thin film 2 having the palladium colloidlayer 3 within the channel 5 to deposit a conductive metal layer 7within the channel 5.

The electroless plating solution used herein is as previously described.Appropriate contact conditions with the electroless plating solutioninclude a temperature of 15 to 120° C., especially 25 to 85° C. and atime of 1 minute to 16 hours, especially 10 to 60 minutes. It ispractical to deposit a metal film to a thickness of 0.01 to 100 μm,especially 0.1 to 20 μm although the thickness varies with a particularpurpose.

After step (3), the following step is carried out if desired. Thestructure resulting from step (3) is treated with a solvent for removingthe photosensitive resin layer, or heated for further improving theadhesion between the metal and the substrate. If the photosensitiveresin layer is formed of a polysilane base material, heat treatment iscarried out at high temperatures to convert all polymer layers intoceramic or insulating layers and further stabilize the conductive metallayer formed by electroless plating. As a result, a wiring board havinga more adherent metal pattern is obtained. For example, by the heattreatment at high temperatures of the structure resulting from step (3),all the polymer layers are converted into insulating layers consistingof ceramic material and the conductive metal layer resulting fromelectroless plating is stabilized. The heat treatment is generallyeffected at a temperature of about 200 to 1,200° C. for about 1 minuteto about 24 hours and desirably, at about 300 to 900° C. for about ½ to4 hours. Through the high-temperature treatment, the metal layerresulting from electroless plating acquires a higher conductivity andhardness and the ceramic converted from the polysilane possesses ahigher heat resistance, insulating property and adhesion.

It is noted that by the high-temperature treatment of polysilane,Si-to-Si bonds are severed allowing various elements to be incorporatedtherein so that the material is stabilized. That is, thehigh-temperature treatment leads to the formation of a silicon oxidebase ceramic material if the treatment is effected in an oxidizingatmosphere, typically air, a silicon nitride base ceramic material ifeffected in a reducing atmosphere, typically ammonia gas, or a siliconcarbide base ceramic material if effected in an inert atmosphere,typically argon or in vacuum.

The method according to the fourth embodiment includes the steps of:

(I) forming a thin film of a polysilane with SiH group on a substrateand irradiating light to the thin film for crosslinking the polysilanefor thereby insolubilizing the polysilane,

(II) forming a photosensitive resin layer on the crosslinked polysilanethin film, selectively irradiating light to the layer, and developingthe layer, to thereby form a predetermined pattern of channels in thephotosensitive resin layer so that the crosslinked polysilane thin filmis exposed within the channels, and

(III) contacting a palladium salt with the crosslinked polysilane thinfilm exposed within the channels to form a palladium colloid layer andcontacting an electroless plating solution for thereby forming aconductive metal layer within the channels. There is obtained a printedwiring board having a metal pattern featuring a high degree ofdefinition.

Referring to FIG. 2, step (I) includes forming a SiH group-containingpolysilane thin film 8 on a substrate 1. The polysilane thin film formedon the substrate is preferably formed of a material primarily comprisinga polysilane of the following general formula (2).

(H_(m)R² _(n)X_(p)Si)_(q)  (2)

wherein R² is hydrogen or a substituted or unsubstituted monovalentaliphatic, alicyclic or aromatic hydrocarbon group, X is as defined forR² or an alkoxy group or halogen atom, m is a number of 0.1 to 2, n is anumber of 0 to 1, p is a number of 0 to 0.5, the sum of m+n+p is from 1to 2.5, and q is an integer of 4 to 100,000. Illustrative examples ofthe groups represented by R² and X and the preferred ranges of m, n, pand q are as described above for formula (1).

It is known from Fukushima et al., Chem. Lett., 1998, 347 that uponexposure to light, typically UV radiation, a polysilane having SiH bondsin a molecule represented by formula (2) undergoes crosslinking reactionand turns to be insoluble in solvents. In the method of the fourthembodiment of the invention, a polysilane having SiH bonds in a moleculeundergoes crosslinking reaction and becomes insolubilized upon exposureto UV, and this polymer even after crosslinking by light exposure iseffective for readily reduce a palladium salt to form a palladiumcolloid, which enables formation of a metal film (e.g., of copper) byelectroless plating.

The substrate, the method of forming a polysilane film, the solvent inwhich polysilane is soluble, and the forming conditions are the same asin the third embodiment. The polysilane thin film formed on thesubstrate preferably has a thickness of 0.01 to 100 μm, especially 0.1to 10 μm.

Then, the polysilane thin film 8 on the substrate 1 is irradiated withlight (shown by arrows) whereby the polysilane is crosslinked forinsolubilization, resulting in a crosslinked polysilane thin film 8′.

The light source used herein preferably emits light having a wavelengthof at least 300 nm and may be a UV light source or visible light source.Illustrative examples are continuous spectrum light sources such ashydrogen discharge lamps, rare gas discharge lamps, tungsten lamps, andhalogen lamps, lasers, and discontinuous spectrum light sources such asmercury lamps. Mercury lamps are preferable because of low costs andease of handling. The light source preferably has a light quantity of0.001 to 100 J/cm², especially 0.1 to 1 J/cm², per polysilane filmthickness of 1 μm. A light quantity below the range would result inshort crosslinking whereas a light quantity above the range would bedetrimental to the subsequent formation of a palladium colloid in step(III).

Step (II) includes forming a photosensitive resin layer 4 on thecrosslinked polysilane thin film 8′ on the substrate, selectivelyirradiating light to the layer, and developing the layer, to therebyform a predetermined pattern of channels in the photosensitive resinlayer 4 so that the crosslinked polysilane thin film 8′ is exposedwithin the channel 5. The photosensitive resin layer may be formed as inthe third embodiment and patterned using a patterned photomask 6 as inthe third embodiment.

Similarly, development is effected as in the third embodiment.

The thickness of the photosensitive resin layer is desirably approximateto that of a metal thin film to be formed, typically 0.1 to 10 μm. Sincethe polysilane film absorbs UV radiation and provides anti-reflectioneffect in the exposure step, the pattern shape is well retained.

The light source used herein is preferably a laser such as KrF or ArFlaser or a mercury lamp having a radiation source of 248 to 254 nm inwavelength. A stepper or scanner type exposure equipment having such alight source incorporated therein is preferably used. For the photomask,masks of the Levenson or halftone type based on the phase-shift masktechnology may be used.

Step (III) includes contacting a palladium salt with the groovedphotosensitive resin layer-bearing substrate to form a palladium colloidlayer 9 on the crosslinked polysilane thin film 8′ exposed within thechannel 5, removing the unnecessary palladium salt, and contacting anelectroless plating solution with the palladium colloid layer-bearingcrosslinked polysilane film 8′ for thereby forming a conductive metallayer 7 on the crosslinked polysilane film 8′ within the channel 5.

More specifically, step (III) includes:

step (III-1) of contacting a palladium salt with the structure resultingfrom step (II) to form a palladium colloid layer 9 at least on thecrosslinked polysilane thin film 8′ exposed within the channel 5 in thephotosensitive resin layer 4,

step (III-2) of washing the structure resulting from step (III-1) toremove an unnecessary palladium salt layer 10, and

step (III-3) of contacting an electroless plating solution with thestructure resulting from step (III-2) to form a conductive metal layer 7on the crosslinked polysilane film 8′ and the palladium colloid layer 9within the channel 5.

First described is step (III-1). For contacting the thin film with thepalladium salt, a technique as used in the third embodiment may be usedwhile the palladium salt and its solution used may also be the same asin the third embodiment. Similarly, the palladium salt is contacted withthe polysilane film using a solvent which does not dissolve thepolysilane film, but in which the palladium salt is dissolved ordispersed, thereby forming a palladium colloid layer. In such a solutiontechnique, a solvent which fully dissolves the palladium salt, but doesnot attack the pattern of polysilane is advantageously used. The solventmay be selected from the solvents exemplified in the solution techniqueof the third embodiment as the solvent for dissolving the palladium saltalthough a choice of the solvent depends on the solubility therein of aparticular photosensitive resin used. Of these solvents, alcohols suchas ethanol are favorable when phenylmethylpolysilane is used as thephotosensitive resin.

The palladium salt is dissolved or dispersed in such a solvent. Thestructure having the pattern of channels formed subsequent to exposureis immersed in the solution or dispersion for about 1 second to 10minutes, followed by drying. On the exposed area of the polysilane thinfilm within the patterned channel, which is hydrophilic, the palladiumsalt is reduced into palladium particles. On the unexposed area of thephotosensitive resin layer, no palladium particles are formed. That is,an (unnecessary) palladium salt layer 10 is left on the photosensitiveresin layer 4. In this way, the desirably patterned polysilanefilm-bearing substrate is obtained. Furthermore, if desired, theresulting structure is heat treated at a temperature of about 40 to 200°C. for promoting the reduction of the palladium salt into palladium onthe polysilane thin film. Drying is desirably effected at a temperatureof 10 to 200° C. under atmospheric pressure or in vacuum.

In step (III-2), the structure resulting from step (III-1) is washed toremove the unnecessary palladium salt layer 10. To this end, thestructure is immersed in the solvent which can dissolve the palladiumsalt. Alternatively, the surface of the structure is scraped off bymechanical grinding. The unnecessary palladium salt layer 10 left on thephotosensitive resin layer 4 is readily removed in this way. Whether theremoval step is by dissolution or mechanical grinding, the palladiumcolloid layer within the channel is left intact after the removal stepbecause palladium has been changed from ion to colloid.

In step (III-3), the structure resulting from step (III-2) is contactedwith an electroless plating solution whereby a conductive metal layer 7deposits on the crosslinked polysilane film 8′ and specifically thepalladium colloid layer 9 within the channel 5. The type of electrolessplating solution and the plating conditions are the same as in the thirdembodiment.

After step (III), the structure may be treated as in the thirdembodiment. There is obtained a wiring board having a metal patternfeaturing a high degree of definition.

The wiring board preparing method of the invention can form a metalwiring pattern having improved heat resistance and a high degree ofdefinition by a simple inexpensive process. Specifically, the wiringboard preparing method according to the third embodiment of theinvention can form on any type of resin substrate a metal wiring patternhaving improved adhesion between the metal and the substrate and a highdegree of definition. The wiring board preparing method according to thefourth embodiment of the invention can form a conductive metal layerhaving improved adhesion between the metal and the substrate in apattern having a high degree of definition. There is obtained a boardhaving a high definition metal circuit formed thereon which isapplicable to logic circuits and memory devices. Since the conductivewiring patterns can find use as printed circuit boards, various devices,flexible switches, battery electrodes, solar batteries, sensors,antistatic protective films, electromagnetic shield casings, integratedcircuits, and motor casings, the wiring board preparing method is usefulin the electric, electronic and communication fields.

EXAMPLE

Examples of the invention are given below by way of illustration and notby way of limitation. All parts are by weight.

Synthetic Example 1

Synthesis of phenylhydrogenpolysilane (PPHS)

To a flask purged with argon, a diethyl ether solution ofbis(cyclopentadienyl)dichlorozirconium was added, wherebybis(cyclopentadienyl)dimethylzirconium serving as a catalyst wasprepared in the system. Per mol of thisbis(cyclopentadienyl)dimethylzirconium, 50 mol of phenylsilane wasadded. The mixture was heated and stirred at 100° C. for 24 hours. Amolecular sieve was added to the reaction solution, which was filteredto remove the catalyst. Phenylhydrogenpolysilane having a weight averagemolecular weight of 2,600 was obtained as solids in a substantiallyquantitative manner.

Synthetic Example 2

Synthesis of phenylmethylpolysilane (PMPS)

In a nitrogen stream, 5.06 g (220 mmol) of metallic sodium was added to60 ml of toluene. While heating at 110° C., the mixture was agitated ata high speed for dispersion. To the dispersion, 19.1 g (100 mmol) ofphenylmethyldichlorosilane was slowly added dropwise with stirring.Agitation was continued for 4 hours until the reactant disappeared,completing the reaction. After the reaction solution was allowed to cooldown, the salt was filtered off, and the residue was concentrated,obtaining 10.0 g (crude yield 83%) of a polysilane crude product. Thispolymer was dissolved in 30 ml of toluene again and 120 ml of hexane wasadded whereupon the polymer precipitated and separated. There wasobtained 6.6 g (yield 55%) of phenylmethylpolysilane having a weightaverage molecular weight of 45,000.

Example 1 and Comparative Example 1

In 9.2 g of toluene were dissolved 0.8 g of the polysilane(phenylhydrogenpolysilane, abbreviated as PPHS) synthesized in SyntheticExample 1 and 8 mg of N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane asa CF-silane (corresponding to 1 part of the CF-silane per 100 parts byweight of the polysilane). This polysilane composition was applied ontoa glass fiber-filled epoxy resin substrate by an imprinting, ink jetprinting or lithographic process to form a pattern of silane components,which was dried at 50° C. and 2 mmHg. This is Step 1.

Next, the above substrate was immersed for one minute in a 3% aqueoussolution of palladium chloride and washed with water. The treatedsubstrate was then immersed in an electroless plating solution, whichcontained 20 g of nickel sulfate, 20 g of sodium hypophosphite and 30 gof sodium acetate in 1,000 g of water, at 80° C. for 10 minutes wherebya nickel metal pattern was formed. The substrate was washed with purewater, dried at 60° C. for 5 minutes, and heat treated in nitrogen at150° C. for ½ hour. There was obtained a glass fiber-filled epoxy resinsubstrate having a nickel pattern formed thereon. This is Step 2.

The nickel section of the structure had a conductivity of 1×10⁴ S/cm andthe substrate section had a conductivity of 1×10⁻⁹ S/cm. The nickelpattern had a fineness of 100 μm when the imprinting process was used,10 μm when the ink jet printing process was used, and 20 μm when thelithography was used. The adhesion between the nickel film and thesubstrate was examined using an adhesive tape, finding no peeling.

In Comparative Example 1, the same procedure as above was repeatedexcept that the CF silane was omitted. In the adhesive tape test,partial peeling of the nickel film from the substrate was found. Also,the same procedure as above was repeated except that the polysilane wasomitted. Little nickel deposited on the substrate.

Examples 2-6

The polysilane (PPHS) synthesized in Synthetic Example 1, 0.8 g, and aCF-silane, the type and amount of which are shown in Table l, weredissolved in 9.2 g of toluene to give a 8% solution. This CF-silanecontaining polysilane composition was applied onto a glass fiber-filledepoxy resin substrate by spin coating at 3,000 rpm for 10 seconds anddried at 50° C. and 2 mmHg, forming a thin film of 0.3 μm thick. Theepoxy resin substrate having the polysilane thin film formed thereon wasimmersed for one minute in a 3% ethanol solution of palladium chlorideand then dried for 30 minutes at 350° C. This is Step 1.

The polysilane (phenylmethylpolysilane, abbreviated as PMPS) synthesizedin Synthetic Example 2 was used as a photosensitive resin. The PMPS wasdissolved in toluene to form a 5% solution. This polysilane solution wasapplied onto the quartz glass plate having the CF-silane containing PPHSfilm formed thereon in Step 1, by spin coating at 2,000 rμm for 5seconds. Drying at 50° C. and 2 mmHg gave a photosensitive resin layer.The resulting structure was a substrate on which a pattern was to beformed. The thickness of the CF-silane containing PPHS film and thephotosensitive resin layer combined was 0.6 μm. A photomask waspositioned over the substrate, which was exposed, using a 20-Wlow-pressure mercury lamp, to UV radiation of 254 nm in a light quantityof 10 J/cm². By development with ethanol, the exposed area was removed.This is Step 2.

The structure resulting from Step 2 was then immersed in an electrolessplating solution, which contained 20 g of nickel sulfate, 10 g of sodiumhypophosphite and 30 g of sodium acetate in 1,000 g of water, at 50° C.for 30 minutes whereby a nickel metal circuit was formed. This is Step3.

The structure was washed with pure water, dried at 60° C. for 5 minutes,and heat treated in nitrogen at 150° C. for ½ hour. There was obtained aglass fiber-filled epoxy resin substrate having a nickel pattern formedthereon.

The nickel section of the structure had a conductivity of 1×10⁴ S/cm andthe unexposed section had a conductivity of 1×10⁻¹² S/cm.

The adhesion between the nickel film and the substrate was examined bythe adhesive tape test, with the results being shown in Table 1.

Comparative Example 2

The same procedure as above was repeated except that in Step 1, thepolysilane film was formed using a CF silane-free polysilane. There wasobtained a glass fiber-filled epoxy resin substrate having a nickelpattern formed thereon.

The adhesion between the nickel film and the substrate was examined bythe adhesive tape test, with the results being shown in Table 1.

TABLE 1 CF silane, Adhesive tape test blend amount mg, (pph*) (%adhesion) Example 2 KBM-603 Excellent 8 mg (1) (100)  Example 3 KBM-603Excellent (10) (95) Example 4 KBM-603 Good (50) (60) Example 5 KBM-903Excellent ( 1) (100)  Example 6 KBM-403 Good ( 1) (70) ComparativeExample 2 — Poor ( 5) *parts by weight of CF silane per 100 parts byweight of polysilane

Example 7

The polysilane (PPHS) synthesized in Synthetic Example 1 was dissolvedin toluene to give a 8% solution. The polysilane solution was appliedonto a quartz glass plate by spin coating at 3,000 rpm for 10 secondsand dried at 50° C. and 2 mmHg, forming a thin film of 0.3 μm thick. Theentire surface of the substrate was exposed to UV radiation in a lightquantity of 100 mJ/cm² using a low-pressure mercury lamp of 20 W and analkali glass filter of 0.1 mm thick for cutting UV radiation having awavelength of shorter than 300 nm. By irradiation, the polysilane wascrosslinked and insolubilized. This is Step I.

The polysilane (PMPS) synthesized in Synthetic Example 2 as aphotosensitive resin was dissolved in toluene to form a 5% solution.This polysilane solution was applied onto the quartz glass plate havingthe crosslinked PPHS film formed thereon in Step 1, by spin coating at3,000 rpm for 10 seconds. Drying at 50° C. and 2 mmHg gave aphotosensitive resin layer. The resulting structure was a substrate onwhich a pattern was to be formed. The thickness of the crosslinked PPHSfilm and the photosensitive resin layer combined was 0.6 μm. A photomaskwas positioned over the structure, which was exposed, using alow-pressure mercury lamp of 20 W, to UV radiation of 254 nm in a lightquantity of 5 J/cm². By development with ethanol, the exposed area ofPMPS was removed. This is Step II.

The structure resulting from Step II was contacted with a 3% ethanolsolution of palladium chloride (Step III-1). It was washed with ethanol.The surface of the PMPS layer was ground to remove the palladium on thesurface (Step III-2). This structure was then immersed in an electrolesscopper plating solution at 25° C. for 15 minutes. The electrolessplating solution was a 1:1 (by volume) mixture of a plating solution Acontaining 2.5 g of copper sulfate pentahydrate, 11.3 g of potassiumsodium tartrate pentahydrate, and 2.8 g of potassium hydroxide in 83.4 gof water and a plating solution B containing 7 g of a 37% formalinaqueous solution in 93 g of water. This electroless plating formed acopper circuit having a high degree of pattern definition. This is StepIII-3.

The structure was washed with pure water, dried at 60° C. for 5 minutes,and heat treated at 100° C. for one hour. There was obtained a quartzglass substrate having a conductive layer of copper formed withinchannels (wiring board). The copper circuit section on the quartz glasssubstrate was measured for conductivity and minimum line width. Theconductivity was measured by a four-probe method on the copper film. Theline width of the copper circuit was measured under a microscope. Theresults are given below.

Conductivity: 1×10⁴ S/cm

Minimum line width: 1 μm

It was confirmed that a metal pattern having a high degree of definitionwas obtained.

Comparative Example 3

A quartz glass substrate was processed as in Example 7 except that thestep of light irradiation for crosslinking was omitted from Step I. Onthe resulting substrate, copper was present only at the boundary betweenthe exposed and unexposed areas and no copper formed on the exposed andunexposed areas.

Comparative Example 4

A quartz glass substrate was processed as in Example 7 except that thestep of light irradiation for crosslinking was omitted from Step I andthe step of PMPS surface grinding was omitted from Step III-2. Thecopper circuit section on the quartz glass substrate was measured forconductivity and minimum line width by the same procedures as above. Theresults are given below.

Conductivity: 1×10⁴ S/cm

Minimum line width: 20 μm

Japanese Patent Application Nos. 10-300894 and 10-309793 areincorporated herein by reference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

What is claimed is:
 1. A method for preparing a wiring board comprisingthe steps of: (1) forming on a substrate a thin film of a polysilanecomposition comprising a polysilane and an amino group-containingalkoxysilane and contacting a palladium salt with a surface of thepolysilane thin film to form a palladium colloid layer thereon, (2)forming a photosensitive resin layer on the polysilane thin film havingthe palladium colloid layer, selectively irradiating light to the layer,and developing the layer, to thereby form a predetermined pattern ofchannels in the photosensitive resin layer so that the polysilane thinfilm having the palladium colloid layer is exposed within the channels,and (3) contacting an electroless plating solution with the polysilanethin film having the palladium colloid layer exposed within thechannels, for thereby forming a conductive metal layer within thechannels.
 2. The method of claim 1 wherein the polysilane is of thefollowing formula (1): (R¹ _(m)R² _(n)X_(p)Si)_(q)  (1) wherein R¹ andR² each are hydrogen or a substituted or unsubstituted monovalentaliphatic, alicyclic or aromatic hydrocarbon group, X is hydrogen or asubstituted or unsubstituted monovalent aliphatic, alicyclic or aromatichydrocarbon group, alkoxy group or halogen atom, m is a number of 0.1 to2, n is a number of 0 to 1, p is a number of 0 to 0.5, the sum of m+n+pis from 1 to 2.5, and q is an integer of 4 to 100,000.
 3. A method forpreparing a wiring board comprising the steps of: (I) forming a thinfilm of polysilane with SiH group on a substrate and irradiating lightto the thin film for crosslinking the polysilane for therebyinsolubilizing the polysilane, (II) forming a photosensitive resin layeron the crosslinked polysilane thin film, selectively irradiating lightto the layer, and developing the layer, to thereby form a predeterminedpattern of channels in the photosensitive resin layer so that thecrosslinked polysilane thin film is exposed within the channels, and(III) contacting a palladium salt with the crosslinked polysilane thinfilm exposed within the channels to form a palladium colloid layer andcontacting an electroless plating solution for thereby forming aconductive metal layer within the channels.
 4. The method of claim 3wherein the polysilane is of the following formula (2): (H_(m)R²_(n)X_(p)Si)_(q)  (2) wherein R² is hydrogen or a substituted orunsubstituted monovalent aliphatic, alicyclic or aromatic hydrocarbongroup, X is hydrogen or a substituted or unsubstituted monovalentaliphatic, alicyclic or aromatic hydrocarbon group, alkoxy group orhalogen atom, m is a number of 0.1 to 2, n is a number of 0 to 1, p is anumber of 0 to 0.5, the sum of m+n+p is from 1 to 2.5, and q is aninteger of 4 to 100,000.
 5. The method of claim 3 wherein in step (I),the polysilane thin film on the substrate is irradiated with light in anexposure of 0.001 to 100 J/cm².
 6. The method of claim 3 wherein theelectroless plating solution contains a copper or nickel ion.